Thank you for your posting, I have got the cover off. I found the best way to do it is to use the thumb and forefinger of one hand to push down on the corners, and use the other hand to pull up the middle This bends the cover, and the catches on the corners come free.
Perfect!
I just hope your upgrade will be successful. If there is some problem let us know and just start new thread.
Bye and happy New Year.